// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/dns/mdns_cache.h"

#include <algorithm>
#include <tuple>
#include <utility>

#include "base/strings/string_number_conversions.h"
#include "net/dns/dns_protocol.h"
#include "net/dns/record_parsed.h"
#include "net/dns/record_rdata.h"

// TODO(noamsml): Recursive CNAME closure (backwards and forwards).

namespace net {

// The effective TTL given to records with a nominal zero TTL.
// Allows time for hosts to send updated records, as detailed in RFC 6762
// Section 10.1.
static const unsigned kZeroTTLSeconds = 1;

MDnsCache::Key::Key(unsigned type, const std::string& name,
    const std::string& optional)
    : type_(type)
    , name_(name)
    , optional_(optional)
{
}

MDnsCache::Key::Key(
    const MDnsCache::Key& other)
    : type_(other.type_)
    , name_(other.name_)
    , optional_(other.optional_)
{
}

MDnsCache::Key& MDnsCache::Key::operator=(
    const MDnsCache::Key& other)
{
    type_ = other.type_;
    name_ = other.name_;
    optional_ = other.optional_;
    return *this;
}

MDnsCache::Key::~Key()
{
}

bool MDnsCache::Key::operator<(const MDnsCache::Key& other) const
{
    return std::tie(name_, type_, optional_) < std::tie(other.name_, other.type_, other.optional_);
}

bool MDnsCache::Key::operator==(const MDnsCache::Key& key) const
{
    return type_ == key.type_ && name_ == key.name_ && optional_ == key.optional_;
}

// static
MDnsCache::Key MDnsCache::Key::CreateFor(const RecordParsed* record)
{
    return Key(record->type(),
        record->name(),
        GetOptionalFieldForRecord(record));
}

MDnsCache::MDnsCache()
{
}

MDnsCache::~MDnsCache()
{
}

const RecordParsed* MDnsCache::LookupKey(const Key& key)
{
    RecordMap::iterator found = mdns_cache_.find(key);
    if (found != mdns_cache_.end()) {
        return found->second.get();
    }
    return nullptr;
}

MDnsCache::UpdateType MDnsCache::UpdateDnsRecord(
    std::unique_ptr<const RecordParsed> record)
{
    Key cache_key = Key::CreateFor(record.get());

    // Ignore "goodbye" packets for records not in cache.
    if (record->ttl() == 0 && mdns_cache_.find(cache_key) == mdns_cache_.end())
        return NoChange;

    base::Time new_expiration = GetEffectiveExpiration(record.get());
    if (next_expiration_ != base::Time())
        new_expiration = std::min(new_expiration, next_expiration_);

    std::pair<RecordMap::iterator, bool> insert_result = mdns_cache_.insert(std::make_pair(cache_key, nullptr));
    UpdateType type = NoChange;
    if (insert_result.second) {
        type = RecordAdded;
    } else {
        if (record->ttl() != 0 && !record->IsEqual(insert_result.first->second.get(), true)) {
            type = RecordChanged;
        }
    }

    insert_result.first->second = std::move(record);
    next_expiration_ = new_expiration;
    return type;
}

void MDnsCache::CleanupRecords(
    base::Time now,
    const RecordRemovedCallback& record_removed_callback)
{
    base::Time next_expiration;

    // We are guaranteed that |next_expiration_| will be at or before the next
    // expiration. This allows clients to eagrely call CleanupRecords with
    // impunity.
    if (now < next_expiration_)
        return;

    for (RecordMap::iterator i = mdns_cache_.begin();
         i != mdns_cache_.end();) {
        base::Time expiration = GetEffectiveExpiration(i->second.get());
        if (now >= expiration) {
            record_removed_callback.Run(i->second.get());
            mdns_cache_.erase(i++);
        } else {
            if (next_expiration == base::Time() || expiration < next_expiration) {
                next_expiration = expiration;
            }
            ++i;
        }
    }

    next_expiration_ = next_expiration;
}

void MDnsCache::FindDnsRecords(unsigned type,
    const std::string& name,
    std::vector<const RecordParsed*>* results,
    base::Time now) const
{
    DCHECK(results);
    results->clear();

    RecordMap::const_iterator i = mdns_cache_.lower_bound(Key(type, name, ""));
    for (; i != mdns_cache_.end(); ++i) {
        if (i->first.name() != name || (type != 0 && i->first.type() != type)) {
            break;
        }

        const RecordParsed* record = i->second.get();

        // Records are deleted only upon request.
        if (now >= GetEffectiveExpiration(record))
            continue;

        results->push_back(record);
    }
}

std::unique_ptr<const RecordParsed> MDnsCache::RemoveRecord(
    const RecordParsed* record)
{
    Key key = Key::CreateFor(record);
    RecordMap::iterator found = mdns_cache_.find(key);

    if (found != mdns_cache_.end() && found->second.get() == record) {
        std::unique_ptr<const RecordParsed> result = std::move(found->second);
        mdns_cache_.erase(key);
        return result;
    }

    return std::unique_ptr<const RecordParsed>();
}

// static
std::string MDnsCache::GetOptionalFieldForRecord(const RecordParsed* record)
{
    switch (record->type()) {
    case PtrRecordRdata::kType: {
        const PtrRecordRdata* rdata = record->rdata<PtrRecordRdata>();
        return rdata->ptrdomain();
    }
    default: // Most records are considered unique for our purposes
        return "";
    }
}

// static
base::Time MDnsCache::GetEffectiveExpiration(const RecordParsed* record)
{
    base::TimeDelta ttl;

    if (record->ttl()) {
        ttl = base::TimeDelta::FromSeconds(record->ttl());
    } else {
        ttl = base::TimeDelta::FromSeconds(kZeroTTLSeconds);
    }

    return record->time_created() + ttl;
}

} // namespace net
